In a study of how animals recognize numbers, chicks prefer a panel showing a small number of dots to be on their left-hand side and a larger number on their right. This suggests that the left-to-right representation of numbers in animals could be similar to that of humans.

Rosa Rugani at the University of Padua in Italy and her colleagues trained domestic chicks (Gallus gallus) to recognize a panel showing five dots. When smaller arrays of only two dots were placed on each side of the chicks, they chose the left array about 70% of the time and the right-hand one roughly 30% of the time. When presented with larger arrays of eight dots, the chicks preferred the one on the right. However, when trained to recognize 20 target dots, the birds went to the left when shown eight dots.

This left-to-right mapping of numbers may have evolved because of brain asymmetry in vertebrates, with numerical processing residing in the right hemisphere.

Science 347, 534–536 (2015)